Replace the upper and lower at the same time. Just drain the antifreeze from the lower hose into a good sized catch pan or bucket. Dispose of properly and keep away from pets and children.
When putting the new hoses back on, make sure the clamps are over the same place that they were with the old hose. Measure from the radiator to the hose clamp to be sure. Do NOT overtighten the hose clamps, the radiator is plastic and can crack!
After fitting the bottom hose, pour the new mix into the engine and radiator until full, attach upper hose, then fill the overflow bottle. Squeeze the upper hose a few times to try to get any air bubbles out. Start the car and check for leaks.
Keep some mix handy, you might have to add some to the overflow bottle after the engine cools down.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)